1. Field of the Invention:
The present invention relates generally to a compressor for compressing a refrigerant. More particularly, the present invention relates to a refrigerant compressor in which 1,1,1,2-tetrafluoroethane or 1,1-difluoroethane is employed as the refrigerant.
2. Description of the related art:
Generally, a refrigerant compressor is used for an air conditioner, a refrigerator or the like so as to blow cool air or warm air into the interior of a room, a vehicle's cabin or the like. A hermetic refrigerant compressor and a semihermetic refrigerant compressor have been hitherto known as the refrigerant compressor, for a car air conditioner.
For example, the hermetic refrigerant rotary compressor includes a motor mechanism and a compressing mechanism which are arranged in a casing. The motor mechanism is operatively connected to the compressing mechanism via a shaft so that the compressing mechanism is driven by the motor mechanism via the shaft.
The compressing mechanism may, for example, include a cylinder and a roller eccentrically fixedly mounted on the shaft which is rotatably disposed in the cylinder. In addition, the compressing mechanism includes a blade which is protruded through the cylinder. One end of the blade is brought in slidable contact with the outer surface of the roller by the resilient force of a spring. The blade serves to divide the interior of the cylinder into a suction chamber and a discharge chamber. As the shaft is rotated, the roller repeatedly performs planetary movement to compress a refrigerant. The refrigerant which has been compressed is first discharged into the casing, and thereafter it is delivered to a refrigerator via a discharge tube. Slidable members such as a roller, a blade and so forth are constructed such that they smoothly move in the presence of a refrigerator oil which is received and stored in the casing. Things are the same with the shaft.
Dichloromethane (hereinafter referred to as CFC 12) and chlorodifluoromethane (hereinafter referred to as HCFC 22) have been mainly employed as the refrigerant in the refrigerant compressor. Further, a naphthene-based mineral oil and a paraffin-based oil each having solubility relative to the CFC 12 and the HCFC 22 have been employed as the refrigerator oil to be received in the compressing mechanism.
In recent years, it has been clarified that a flon discharged from each of the aforementioned refrigerants has serious effects on human beings as well as animals and plants. For this reason, it has been determined, on a global base, that employment of the CFC 12 and others, each having a high ozone depletion potential, is to be reduced year by year and employment of the aforementioned refrigerants will be prohibited in the future. In view of the foregoing circumstances, 1,1,1,2-tetrafluoroethane (hereinafter referred to as HFC 134a), 1,1-difluoroethane (hereinafter referred to as HFC 152a) and the like have been developed to be substituted for the CFC 12. In practice, the HFC 134a, the HFC 152a and the like have a low ozone depletion potential, respectively. However, they are hardly dissolved in the mineral oil which has heretofore been used as the refrigerator oil. For this reason, endeavors have been made to use a polyether-based oil, a polyester-based oil, a fluorine-based oil or the like, each having compatibility with HFC 134a and the HFC 152a when they are used as a refrigerant.
However, in the case where the HFC 134a or the HFC 152a is used as a refrigerant, to be substituted for the CFC 12 and, e.g., a polyether-based oil or a polyester-based oil is used as the refrigerator oil having solubility relative to the foregoing refrigerant, there arises a problem in that slidable members in the compressing mechanism or the like in the refrigerant compressor are greatly worn as the refrigerant compressor is operated. This problem leads to the result that the refrigerant compressor can not be stably operated for a long time.
Components in the refrigerant compressor which will be worn are classified into two groups, one of them being the shaft and associated components, and the other one being the blade, the roller (or the piston) and associated components. The shaft is rotated at a high rotational speed while it receives a spring force and a pressure in the cylinder via a roller and thereby it is slightly bent or curved due to slidable contact with a frame and a bearing, each serving to rotatably support the shaft. Consequently, the outer surface of the shaft and the inner surface of the bearing are unavoidably worn as the refrigerant compressor is driven. On the other hand, the blade rubs against the inner surface of a through aperture formed in the cylinder, due to the differential pressure between the two divided chambers in the cylinder, causing both the blade and the cylinder to be worn. In addition, since the foremost end of the blade is normally squeezed against the roller by the resilient force of the spring, the outer surface of the roller is worn too.
To fabricate slidable members such as a shaft or the like, a cast iron (e.g., JIS FC 25 specified in accordance with Japanese Industrial Standard (hereinafter referred to simply as FC 25)), a carbon steel (e.g., S12C, S15C or the like), a carbon steel for cold heading and cold forging (e.g., SWRCH 10A, SWCH 15A or the like), a carbon steel for machine structural use (SCM 435H or the like), a stainless steel, a sintered alloy and similar metallic materials have heretofore been used. However, it has been found that the carbon steel and others are greatly worn as the refrigerant compressor is operated with the use of the refrigerant and the refrigerator oil as mentioned above. Once the slidable members in the refrigerant compressor are worn, the ability to compress the refrigerant is degraded. As a result, it becomes difficult to operate the refrigerant compressor properly.
It is considered that wear of the slidable members is caused for the following reasons.
Specifically, in the case where CFC 12 is used as refrigerant, chlorine atoms in the CFC 12 react with iron atoms in each slidable member to thereby form a film of iron chloride having excellent wear resistance. In contrast with the CFC 12, in the case where HFC 134a is used as the refrigerant, since the HFC 134a contains no chlorine atom, a film of lubricant, such as the film of iron chloride, is not formed due to the absence of chlorine atoms, resulting in the lubricating function being deteriorated. On the other hand, since a conventional mineral oil-based refrigerator oil contains a cyclic compound, it has a comparatively high ability of forming an oil film. On the contrary, since the refrigerator oil having compatibility with HFC 134a or HFC 152a is composed of a cyclic compound as a main substance, it can not maintain an oil film having a certain adequate thickness under severe slidable conditions.
A carbon steel widely used as a material for slidable members is normally plastically processed in the form of a cold heading and has a Vickers hardness within the range of 300 to 500. After completion of the cold heading, the carbon steel has work hardness and exhibits a cold-rolled structure in which crystalline grains are elongated in the direction of working. FIG. 10 is a microscopic photograph which illustrates a macrostructure of the cold-rolled structure of the carbon steel on the surface of a cut piece thereof (refer to page 38 in the Section on steel materials in Collection Of Microscopic Photographs, 1979 edition, each illustrating a macrostructure of each of the steel material, edited by the Japan Metallic Material Association). In FIG. 10, the crystalline grains elongating in the direction of rolling with a white color represent a ferrite, and the crystalline grains remaining between the white crystalline grains while exhibiting a black color represent a perlite, respectively. Since the carbon steel having the aforementioned grain structure is forcibly pulled during a rolling operation, a residual stress remains within the carbon steel, causing the carbon steel to be kept in the thermally unstable state.
Therefore, the surface structure of a slidable member fabricated by using the carbon steel kept in the thermally unstable state is readily peeled off from the surface of the substrate for the above-described reasons, unless a film of lubricant is satisfactorily formed on the surface of the substrate of the carbon steel. Once peeling has occurred, grains peeled off therefrom act as burrs and scrape the surface of opposed slidable members. As a result, the wear loss of the carbon steel is increased.
In addition, HFC 134a, HFC 152a and the refrigerator oils compatible with them have high moisture absorbability. Since the refrigerant and the refrigerator oil normally recirculate through the casing, a film of lubricant on the surface of each slidable member is decomposed as the quantity of water in the refrigerant and the refrigerator oil increases. As a result, corrosive wear occurs with the slidable members. Indeed, the corrosive wear proceeds at an accelerated speed. Consequently, reduction of wear resistance of the slidable members is promoted.
Therefore, many requests have been received from users for improving wear resistance of the slidable members in the refrigerant compressor when HFC 134a or HFC 152a are employed as a new refrigerant, to be substituted for CFC 12, and a refrigerator oil having compatibility with the foregoing refrigerants are used in the refrigerant compressor. In addition, another important subject is to make it possible to operate the compressor for a long time by improving wear resistance of the slidable members.